By: Steve Bush October 22, 2021
The open source grbl project has produced software that allows Arduino to control three-axis CNC machines-it is the software in "3018" and related low-cost CNC desktop routers made in China.
It is appreciated for the ability of its developers to squeeze into 16MHz 8-bit AVR microcontrollers and their ingenuity in doing so. As people use it as the basis for more and more complex and advanced CNC projects, related hardware has begun to show its advantages. age.
grblHAL is one of grbl's open source 32-bit processes and is becoming more and more popular because it interacts with its host in the same way as grbl, while running on various 32-bit processors over 100MHz.
From the point of view of CNC mechanics: grblHAL-based hardware can output much more step and direction pulses to more than three stepper motors per second than grbl-on-AVR.
grblHAL is divided into two parts: the easy-to-port hardware abstraction layer (the HAL in the name comes from here) and the instruction fetching digital computing core (right picture).
Although this is not well known to many "serious" CNC users-they are more accustomed to Mach4, Mach3 or LinuxCNC on the PC-but my guess is that when people realize they no longer need to be from the PC When the PC outputs high-rate pulses, grblHAL will quickly attract attention. Milling machine or router.
In my limited understanding, a PC (or Raspberry Pi) is still needed to send commands to grblHAL, but this can be connected to grblHAL hardware via a standard USB or Ethernet that is not too burdensome. And with a smaller size, the grblHAL hardware can now be located next to the stepper drive, keeping fast pulses within a short local connection. If I am mistaken, please correct me in the comments.
The community has ported it to multiple processors, "terjeio" is developing a branch for the Raspberry Pi Pico board, specifically using it to use the new PIO serial data coprocessor built into the onboard Raspberry Pi RP2040 MCU. Send the appropriate signal.
It seems that phil-barrett is cooperating to develop a breakout board called PicoCNC, which will accept Raspberry Pi Pico and convert its IO to the correct voltage to drive four step controllers and auxiliary equipment, and optically isolated input from CNC machine tools and handle Pico's power supply.
The reason why phil-barret is important is that as Brookwood Design, phil-barrett is already a powerful (600MHz Cortex-M7) Teensy 4.1 MCU-on-module-which can control up to five axes, which can be provided by Tindie as part of the kit.
Tribute to the innovative grbl open source community.
By the way, the only productive comment I may be qualified to make to anyone designing breakout boards for electrical noise environments (correct me if you know this is a waste of time-Mr. Coulter?), not one A single resistor in series with the LED of the optocoupler is used for isolated 12V or 5V input. I will divide the resistor into two equal parts and place one in each lead to the optocoupler LED to prevent noise from being low- The resistor is routed to the pcb (connected along the non-resistive).
Teensy 4.1 CNC board by Brookwood Design on Tindie
The image is taken from the linked grbl and Tindie pages. If this is used incorrectly, I am sorry, please contact us and I will delete them.
Tagged as: Controlling EinW Engineer Wonderland Machinery
Steve, thank you for your writing. Your comments are correct. The only minor correction I will make is that I have sold nearly 600 Teensy-based boards and have many users.
Your noise comment about dividing the resistor into two parts is valuable. However, because it is located on the isolated side, noise does not enter the digital part.
I am excited about the picoCNC board, because the total cost of the CNC controller is only slightly higher than the cost of the Arduino plus shield, and the performance is about 10 times that of it. But the real benefit is to expand the accessibility of grblHAL software, which is comparable in performance and functionality to Mach 4 and LinuxCNC.
Thanks to phil-barrett for the update-now included above there is an impressive project between you and terjeio-if I missed the other major contributors, please forgive me. Regarding the shunt resistor, I agree with you, it is a digital board. If it were an RF or sensitive analog circuit, I would be more worried-surprisingly low impedance fast edge coupling between the tracks on the PCB. I hope the clever Mr. Kurt can comment, because he knows EMC's black magic best. Good luck to PicoCNC
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